Composer is a dependency manager for PHP (similar to npm for Node.js or pip for Python). Composer will pull in all the required PHP packages your project depends on and manage them for you. This tutorial provides the steps necessary to install Composer on Debian 9 systems. We will also cover how to use Composer to create and manage PHP projects. Prerequisites Before continuing with this tutorial, make sure you are logged in as a user with sudo privileges and you have PHP installed on your Debian 9 system.